Re: [Qemu-devel] [kvm-unit-tests PATCHv6 2/3] arm: pmu: Check cycle count increases

[Christopher Covington]

Hi Wei,

On 10/12/2016 11:49 AM, Wei Huang wrote:
> On 10/11/2016 01:40 PM, Christopher Covington wrote:
>> Ensure that reads of the PMCCNTR_EL0 are monotonically increasing,
>> even for the smallest delta of two subsequent reads.
>>
>> Signed-off-by: Christopher Covington <address@hidden>
>> Reviewed-by: Andrew Jones <address@hidden>
>> ---
>>  arm/pmu.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 60 insertions(+)
>>
>> diff --git a/arm/pmu.c b/arm/pmu.c
>> index 42d0ee1..4334de4 100644
>> --- a/arm/pmu.c
>> +++ b/arm/pmu.c
>> @@ -14,6 +14,8 @@
>>   */
>>  #include "libcflat.h"
>>  
>> +#define NR_SAMPLES 10
>> +
>>  #if defined(__arm__)
>>  static inline uint32_t get_pmcr(void)
>>  {
>> @@ -22,6 +24,25 @@ static inline uint32_t get_pmcr(void)
>>      asm volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (ret));
>>      return ret;
>>  }
>> +
>> +static inline void set_pmcr(uint32_t pmcr)
>> +{
>> +    asm volatile("mcr p15, 0, %0, c9, c12, 0" : : "r" (pmcr));
>> +}
>> +
>> +/*
>> + * While PMCCNTR can be accessed as a 64 bit coprocessor register, 
>> returning 64
>> + * bits doesn't seem worth the trouble when differential usage of the 
>> result is
>> + * expected (with differences that can easily fit in 32 bits). So just 
>> return
>> + * the lower 32 bits of the cycle count in AArch32.
>> + */
>> +static inline unsigned long get_pmccntr(void)
>> +{
>> +    unsigned long cycles;
>> +
>> +    asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r" (cycles));
>> +    return cycles;
>> +}
>>  #elif defined(__aarch64__)
>>  static inline uint32_t get_pmcr(void)
>>  {
>> @@ -30,6 +51,19 @@ static inline uint32_t get_pmcr(void)
>>      asm volatile("mrs %0, pmcr_el0" : "=r" (ret));
>>      return ret;
>>  }
>> +
>> +static inline void set_pmcr(uint32_t pmcr)
>> +{
>> +    asm volatile("msr pmcr_el0, %0" : : "r" (pmcr));
>> +}
>> +
>> +static inline unsigned long get_pmccntr(void)
>> +{
>> +    unsigned long cycles;
>> +
>> +    asm volatile("mrs %0, pmccntr_el0" : "=r" (cycles));
>> +    return cycles;
>> +}
>>  #endif
>>  
>>  struct pmu_data {
>> @@ -72,11 +106,37 @@ static bool check_pmcr(void)
>>      return pmu.implementer != 0;
>>  }
>>  
>> +/*
>> + * Ensure that the cycle counter progresses between back-to-back reads.
>> + */
>> +static bool check_cycles_increase(void)
>> +{
>> +    struct pmu_data pmu = {0};
> 
> Compilation error on my machine:
> 
> arm/pmu.c: In function ‘check_cycles_increase’:
> arm/pmu.c:148:9: error: missing braces around initializer
> [-Werror=missing-braces]
>   struct pmu_data pmu = {0};
> 
> Same for Patch 3.

"...So your compiler complains about {0}? Is there a problem besides the
warning? If not, then I'm still a bit inclined to keep the code neat. The
warnings will go away with compiler updates."

https://lists.gnu.org/archive/html/qemu-devel/2015-10/msg06064.html

Thanks,
Cov
-- 
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm
Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code
Aurora Forum, a Linux Foundation Collaborative Project.